1 不定式作宾语
1) 动词+ 不定式
afford, aim, appear, agree, arrange, ask, be, decide, bother, care, choose, come, dare, demand, desire, determine, expect, elect, endeavor¹, hope, fail, happen, help, hesitate, learn, long, mean, manage, offer, ought, plan, prepare, pretend, promise, refuse, seem, tend, wait, wish, undertake

The driver failed to see the other car in time.　司机没能及时看见另一辆车。
I happen to know the answer to your question.　我碰巧知道你那道问题的答案。

2) 动词+不定式；动词+宾语+不定式
ask, beg, choose, expect, hate, help intend like, love, need prefer, prepare, promise, want, wish

I like to keep everything tidy.　我喜欢每件东西都保持整洁。
I like you to keep everything tidy.　我喜欢你使每件东西都保持整洁。
I want to speak to Tom.　 我想和汤姆谈话。
I want you to speak to Tom.　 我想让你和汤姆谈话。

3) 动词+疑问词+ to
decide, know, consider forget, learn, remember, show, understand, see, wonder, hear, find out, explain, tell　　

Please show us how to do that. 请演示给我们如何去做。
There are so many kinds of tape-recorders on sale that I can't make up my mind which to buy.有这么多的录音机，我都拿不定主意买哪一种。

注意
疑问词带不定式在句中作成分时，谓语动词用单数。如：The question is how to put it into practice. 问题是怎样把它付诸实施。

2. 不定式作补语
1) 动词+宾语+不定式(to do)
advise, allow, appoint, believe, cause, challenge, command, compel², consider, declare, drive, enable³, encourage, find, forbid, force, guess, hire, imagine, impel⁴, induce⁵, inform, instruct, invite, judge, know, like, order, permit, persuade, remind, report, request, require, select, send, state, suppose, tell, think, train, trust, understand, urge, warn

a.Father will not allow us to play on the street.　父亲不让我们在街上玩耍。
b.We believe him to be guilty. 我们相信他是有罪的。

Find 的特殊用法
Find 后可用分词做宾补，或先加形式宾语，再加形容词，最后加带to 的动词不定式。find后也可带一个从句。此类动词还有get，have。

I found him lying on the ground.
I found it important to learn.
I found that to learn English is important.

典型例题
The next morning she found the man ___ in bed，dead.　
A. lying　 B. lie　 C. lay　 D. laying　　
答案：A.find的宾语后面，用分词或分词短语，起宾语补足语作用。现在分词表达主动，也表达正在进行，过去分词表达被动。

2) to + be 的不定式结构，作补语的动词。
acknowledge⁶, believe, consider, think, declare(声称), discover, fancy(设想), feel, find,　guess, judge, imagine, know, prove, see(理解), show, suppose, take(以为), understand 

We consider Tom to be one of the best students in our class. 我们认为汤姆是班上最好的学生之一。

典型例题
Charles Babbage is generally considered　___ the first computer.　
A. to invent　B. inventing　 C. to have invented　 D. having invented　
答案：A. 由consider to do sth. 排除B、D。. 此句只说明发明这一个事实，不定式后用原形即可。而C为现在完成时，发明为点动词一般不用完成时，且此处也不强调对现在的影响，因此不选C。

3) to be +形容词
seem, appear, be said, be supposed, be believed, be thought, be known, be reported, hope, wish, desire, want, plan, expect, mean

The book is believed to be uninteresting.　人们认为这本书没什么意思。

4) there be+不定式
believe, expect, intend, like, love, mean, prefer, want, wish, undrstand

We didn't expect there to be so many people there. 我们没料到会有那么多人在哪里。

注意
有些动词需用as 短语做补语，如regard, think believe, take, consider.
We regard Tom as our best teacher.　我们认为汤姆是我们最好的老师。
Mary took him as her father .　玛丽把他当作自己的父亲。

3. 不定式作主语
1) It's easy (for me) to do that. 我做这事太容易了。
easy, difficult, hard, important, possible, impossible, comfortable, necessary, better;
the first, the next, the last, the best, too much, too little, not enough

It's so nice to hear your voice.　听到你的声音真高兴。
It's necessary for you to lock the car when you do not use it. 当你不用车的时候，锁车是有必要的。

2) It's very kind of you to help us. 他帮助我们，他真好。
kind, nice, stupid, rude, clever, foolish, thoughtful⁷, thoughtless⁸, brave, considerate(考虑周到的), silly, selfish(自私的)

It was silly of us to believe him.　我们真愚蠢，竟然相信了他。
It seemed selfish of him not to give them anything.　他不给他们任何东西，这显得太自私了。

注意
1) 其他系动词如，look，appear等也可用于此句型
2) 不定式作为句子成分时，动词用单数形式。
3) 当不定式作主语的句子中又有一个不定式作表语时，不能用It is… to…的句型
(对)To see is to believe.　百闻不如一见。(错)It is to believe to see.

It's for sb.和 It's of sb.
1) for sb. 常用于表示事物的特征特点，表示客观形式的形容词，如easy, hard, difficult,　 interesting, impossible等：
It's very hard for him to study two languages. 对他来说学两门外语是很难的。
2) of sb的句型一般用表示人物的性格，品德，表示主观感情或态度的形容词，如good, kind, nice, clever, foolish, right。
It's very nice of you to help me. 你来帮助我，你真是太好了。

for 与of 的辨别方法
用介词后面的代词作主语，用介词前边的形容词作表语，造个句子。如果道理上通顺用of，不通则用for。如：You are nice.　(通顺，所以应用of)。He is hard.　(人是困难的，不通，因此应用for。)

5. 不定式作定语
不定式做定语通常要放在被修饰的词后。例如：
I have a lot of work to do.　
So he made some candles to give light.

6. 不定式作状语
1) 目的状语　
To… only to (仅仅为了), in order to, so as to, so(such)… as to… (如此……以便……)
He ran so fast as to catch the first bus.　他飞快地跑以便赶上第一班车。
I come here only to say good-bye to you.　我来仅仅是向你告别。

2) 作结果状语，表事先没有预料到的，要放在句子后面。
What have I said to make you angry.
He searched the room only to find nothing.

3) 表原因
I'm glad to see you.

典型例题
The chair looks rather hard, but in fact it is very comfortable to ___.　
A. sit　 B. sit on　 C. be seat　 D. be sat on
答案：B.　如果不定式为不及物动词，其后应有必要的介词。当动词与介词连用时，常位于"形容词+动词不定式"结构的末尾。

用作介词的to
to 有两种用法：一为不定式+动词原形； 一为介词+名词/动名词, to 在下面的用法中是第二种，即to+ 名词/动名词：admit to承认，confess to承认，be accustomed to 习惯于，be used to 习惯于，stick to 坚持，turn to开始，着手于，devote oneself to 献身于，be devoted⁹ to 致力于， look forward to 盼望，pay attention to

注意
省to 的动词不定式

1) 情态动词 ( 除ought 外，ought to)：
2) 使役动词 let, have, make：
3) 感官动词 see, watch, look at, notice , observe, hear, listen to, smell, feel, find 等后作宾补，省略to。
　
注意
在被动语态中则to 不能省掉。
I saw him dance. =He was seen to dance.
The boss made them work the whole night.=They were made to work the whole night.
4) would rather，had better：
5) Why… / why not…：
6) help 可带to，也可不带to, help sb (to) do sth：
7) but和except：but前是动词do时，后面出现的动词用不带to的动词不定式。
8) 由and, or和than连接的两个不定式，第二个to 可以省去：
9) 通常在discover, imagine, suppose, think, understand等词后，可以省去to be：He is supposed (to be) nice.　他应该是个好人。举例：He wants to move to France and marry the girl. He wants to do nothing but go out. 比较：He wants to do nothing but go out. He wants to believe anything but to take the medicine.

典型例题
1) ---- I usually go there by train.　
---- Why not ___ by boat for a change?　
A. to try going　 B.　trying to go　 C.　to try and go　 D.　try going　　
答案：D. why not 后面接不带to 的不定式，因此选D。
2) Paul doesn't have to be made ___. He always works¹⁰ hard.　
A. learn　 B. to learn　 C. learned¹¹　 D. learning¹²
答案：B. make后接不带to 的动词不定式，当其用于被动时，to 不可省略。

动词不定式的否定式
Tell him not to shut the window…　 
She pretended not to see me when I passed by. 我走过的时候，她假装没看见。

典型例题
1) Tell him ___ the window.　
A. to shut not　 B. not to shut　 C. to not shut　 D. not shut　
答案：B。 tell sb to do sth 的否定形式为tell sb not to do sth.
2)　She pretended ___ me when I passed by.　
A.　not to see　 B. not seeing　　C. to not see　 D.　having not seen　
答案：A。 pretend 后应接不定式。其否定形式为pretend not to do sth.。
3) Mrs. Smith warned her daughter ___ after drinking.
A. never to drive　 B. to never driver　C. never driving　 D. never drive　
答案：A。warn sb to do sth. 的否定形式为warn sb not to do sth. 此处用的是否定词never.
4) The boy wanted to ride his bicycle in the street，but his mother told him ____.　
A. not to　　B. not to do　　C. not do it   D. do not to
答案：A。not to 为not to do it 的省略形式。可以只用to这个词，而不必重复整个不定式词组。及物动词do后应有名词、代词等，否则不对，因此B，D不对。
5) The patient was warned ___ oily food after the operation.
A. to eat no　 B. eating not　 C. not to eat　D. not eating
答案：C。warn一词要求后用不定式，此处为不定式的被动，否定形式为be warned not to do。